Diazotype heat development photographic paper comprising a sugar brightening agent



United States Patent 3,166,422 DIAZOTYPE HEAT DEVELQPMENT PHUTO- GRAPHIC PAPER COMPRISILNG A SUGAR ,BRIGHTENING AGENT Q John Joseph McKinney, Binghamton, and Bernard I. Helper-in, Glen Aubrey, N.Y., assignors to General Auiiine & Film Corporation, New York, N.Y., a corporation of Delaware. p t No Drawing. Filed July 1, 1963, Ser. No. 292,114

, 6 Claiuns. (Cl. 96-75) The present invention relates to a diazotype heat de-j It relates velopment photographic paper and process. more particularly to a two-component diazotypej photographic process and the light-sensitive diazotype photoprinting material employed therein which is capable of producing bright and distinct dye images.

The invention makes use of a combination of a lightsensitive diazonium compound and an azo coupling component contained in a coating, which couple to produce an azo dye. The invention, moreover, involves the use of heat developable diazotype and coupler-materials which are physically and chemically stable during ordinary storage and which also have other unique and desirable properties. It involves, more particularly, an improvement in brightness of the dye image, as compared with prior heat development processes.

In the prior art, numerous proposals have been made for various modifications of the original diazotype photographic process. Basically the diazotype process is well known. It involves exposure to actinic light under an original having an opaque pattern on a translucent background of sheet material bearing a light-sensitive diazonium compound, and in two-component material-also an azo coupling component, stabilized with an acid against premature coupling, whereby the diazonium compound is 3,156,422 Patented Jan. 19, 1965 biguanidine salt of a diazo compound which would decompose underthe influence of heat to yield ammonia w as a developing agent. In US. Patent 2,178,771 separate layers were proposed and development by use of steam was suggested. Various other patents have suggested other processes involving heat.

The diazonium salts and couplers are normally applied in such away, e.g., in combination with an acid stabilizer, so that theycannot react until the pH of the system is altered, eg, by application of a basic compound. The latter may be generated or evolved by heating. Such a compound might be one which, when heated, gives rise to an alkaline environment, as in the case of the guanidine compound of the patent mentioned above. In most cases, application of heat produces a dull image.

The use of alkaline generating agents, such as urea or trichlor-oacetic acid-sodium trichloroacetate in an acidic system for coupling has been proposed in the prior art.

destroyed in the light-struck areas, and developing by alkaline treatment to cause coupling of the residual diazonium compound and coupling component forming, an azo dye image in the areas protected by the opaque pattern.

A process which has enjoyed moderate success is a dry diazo process. The dry process of the prior art using two-component diazotype materials commonly makes use of aqueous ammonia at an elevated temperature to promote the coupling reaction. The ammonia is applied in such a manner as to cause the two reactive materials on the supporting sheet to react andthereby to form a water insoluble azo dye. This process has the obvious disadvantages that the odor of ammonia is involved and that the handling of ammonia, usually in the form of aqueous ammonia solutions, is necessary. Also, there are complications in the apparatus necessitated by the use of ammonia. Hence the process, and the necessary equipment, are not always suitable for use, for example, in ofiice reproduction systems where the diazo process otherwise has certain advantages.

The dry developing process, using ammonia, has several practical objections. It requires the purchase and use of a relatively complex development apparatus unit. As a result, diazotype reproducing machines tend to be relatively expensive and thus less competitive economically with other systems. This is particularly true for the relatively simple copying operationswhere convenience and freedom from operating diificulties are so important.

Numerous attempts have been made in the prior art to obviate some of the deficiencies described above. Thus, it has been proposed to prepare and apply the individual Reaction takes place on heating. However, urea decomposes slowly at moderate storage temperatures and even at normal room temperature. Furthermore, relatively large amounts of urea are required for satisfactory development. It is diflicult to store materials of this type and maintain proper quality over moderate periods of time. The trichloroacetic acid-sodium trichloroacetate systemhas not been satisfactory, in general, because the excess trichloroacetic acid usually causes severe degeneration of the paper. In addition, the sodium trichloroacetate itself tends to cause the diazonium salt to decompose prematurely. This complex system is preferably replaced by a single base generating compound such as an alkali metal-, 'ammoniumor nitrogen base salt of trichloroacetic acid. In the aforesaid procedures, the degree of heat required is often such as to drive the normal paper moisture out of the sheet and to cause partial decomposition, concurrcntly with coupling, of the light-sensitive diazonium compound. The loss of this moisture and said decomposition causes formation of dyes that are dull.

Hence, an object of the present invention is to prevent this undesirable loss of brightness in the heat developed dye image. This is accomplished by adding a sugar of the class consisting of sucrose, lactose, cellobiose, rafli nose and mannose or mixtures thereof to the dye forming reactant materials. Surprisingly, these sugars have been found effective to prevent loss of brightness, while other common sugars such as glucose, fructose, maltose and galactose were found to have the opposite elfectreducing the image density. I

The addition of humectants such as glycol and glycerin will, to some extent, reduce or eliminate the loss of dye brightness. However, materials containing these humectants have poor shelf life. According to the present invention sugar such as sucrose may be added to the formulation to improve the brightness without adversely affecting shelf life.

The amount of sucrose or of the other sugars specified above can be varied somewhat but is usually within the range of 5 to 20 times the Weight of the diazonium salt in the formulation, or 2 to 7 times the weight of the azo coupler.

In other respects, the formulations, which include an acid stabilizer such as citric acid so as to prevent premature coupling, and sucrose or equivalent to insure Citric acid gm q. brightness, oifer a number of unique advantages. Such formulations will be illustrated by the examples which follow:

Example 1 Water ml 6 0. N ethyl N 2 hydroxyethyl p aminobenzenediazonium chlorozincate gm 1.0 2,3-dihydroxynaphthalene-6-sodium sulfonate gm 3.0 Sucrose gm Shawinigan RS-4326 (a low viscosity grade of polyvinyl alcohol) gm 5 Sodium trichloroacetate gm 4 National Resyn 1006 (a polyvinyl acetate emulsion) ml 5 Silica (average particle size: 3-6 microns) gm 4 Water to 100 ml.

The above formulation and a formulation identical to the abovebut-not containing sucrose, were. coated on paper by means of conventional equipment. The dried material was exposed to light under an opaque image in the same way as conventional diazotype material, but

developed by passing the sheet over a roller heated to 300 F..350 F. Prints made from material containing sucrose showed superior dye brightness to prints made from Shawinigan RS-4326 (a aqueous solution of a low viscosity grade of polyvinyl alcohol) ml 20 NationalResyn 1006 (a polyvinyl acetate emulsion) ml 5 Water to 100 ml.

The above formulation was coated and dried on conventional equipment. This material was then coated with the following:

Part 2:

Water ml ,60 Sucrose gm-.. 10 2,3 dihydroxynaphthalene 6 -.sodium sulfonate gm 3.0 Sodium trichloroacetate gm 3.0

Onyx Resin Xyno X99 (an aqueous polyvinyl acetate emulsion containing 60% polyvinylacetate) ml Water to 100 ml.

A formulation the same as the above but from which sucrose was omitted was also coated on the Part I'layer.

Dried material was processed to form a copy by heat development in the same manner as described in Example 1. The material containing sucrose resulted in a substantially brighter image than that obtained with material from which sucrose was omitted.

Example 3 The procedure of Example 2 was repeated except that sucrose was removed from Part II solution and added to Part 1 solution. The results were essentially the same. Hence, it does not appear to be particularly critical whether the sucrose is added to the diazonium layer or to 'the coupling layer, when separate coatings or layers chosen from any compounds which have aneutral or acid reaction at normal temperatures provided the substance chosen also gives rise to an alkaline environment upon the application of heat at temperatures of the. order of 100 to 200 C., alkalimetal (-Na, K),-am'monium and nitrogen base trichloroacetates meet these requirements quite satisfactorily and are preferred for the purposes of this invention. a w

I Thedegree of heat required to develop the photograph Will.,depend somewhat on the particular ingredients in the coating material or materials. it should be within a temperature range of to 200 C. and preferably .120 C., and should be applied only for a short period of time, ordinarily of the order of seconds or fractions thereof. The sucrose and other sugars named above, enhance the brightness of single as well as double layer materials as disclosed in the examples. The mechanisrn by which the addition of the sucrose and other sugars produce brightness in the azo dye images is not certain, but it may be that, due to the application of heat, the sugars themselves partially break down and generate moisture, which tends to replace that lost in the paper. In any case, the improvement in the brightness of the image produced by use of sucrose and the other sugars is substantial. Prints made with sucrose are such superior to those produced without it.

It will be obvious that a number of variations may be made in the invention as will readily occur to those skilled in the art. It is intended by the claims which follow to cover such improvements as far as the prior art permits.

We claim:

1. A two-component diazotype photo-printing material having on the surface of a supporting sheet a lightsensitive diazoniurn compound, an azo coupler, an acid stabilizer against premature coupling, a neutral to acid compound which on heating to a temperature of 100 to 200 C. produces an alkaline reaction, and a sugar selected from the class consisting of sucrose, lactose, cellobiose, mannose and raflinose.

2. A two-component diazotype material as defined in claim l-wherein the'sugar is present in an amount from 5-20 times the quantity of said diazonium compound.

3. Atwo-component diazotype photo-printing material as defined in claim 1 wherein the sugar is present in an amount from 2 to 7 times the quantity of said azo coupling component.

No references cited.

Generally speaking, 

1. A TWO-COMPONENT DIAZOTYPE PHOTO-PRINTING MATERIAL HAVING ON THE SURFACE OF A SUPPORTING SHEET A LIGHTSENSITIVE DIAZONIUM COMPOUND, AN AZO COUPLER, AN ACID STABILIZER AGAINST PREMATURE COUPLING, A NEUTRAL TO ACID COMPOUND WHICH ON HEATING TO A TEMPERATURE OF 100 TO 200*C. PRODUCES AN ALKALINE REACTION, AND A SUGARD SELECTED FROM THE CLASS CONSISTING OF SURCROSE, LACTOSE, CELLOBIOSE, MANNOSE AND RAFFINOSE.
 5. A DIAZOTYPE PHOTO-PRINTING MATERIAL AS DEFINED IN CLAIM 1 WHEREIN SAID DIAZONIUM COMPOUND AND SAID ACID TO NEUTRAL COMPOUNDS ARE CONTAINED IN SEPARATE BUT SUPERPOSED CONTIGUOUS LAYERS. 